Vertical HEMT Structure for Higher Breakdown on Si Substrates
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Solution Overview
Problem
Existing high electron mobility transistors (HEMTs) based on Group III nitride semiconductors face limitations due to defects in their structures, which restrict their application ranges, particularly in high energy, high voltage, and high frequency applications.
Innovation Solution
A vertical HEMT structure is developed with a channel layer and a channel supply layer forming a vertical 2DEG adjacent to their interface, along with specific electrode configurations and additional layers like nucleation, buffer, shielding, and insulating layers to enhance performance and reduce substrate influence, allowing for improved voltage withstand and reduced dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional planar HEMT structures are used, then manufacturing is simpler, but voltage withstand capacity and performance in high energy applications are limited
Solution Approach 1:
The patent transitions from a conventional planar (2D) HEMT structure to a vertical (3D) HEMT structure. The channel layer and channel supply layer are arranged vertically with the 2DEG forming at their interface, enabling current flow in the vertical direction. This dimensional change increases the effective channel area and improves voltage withstand capacity while maintaining manufacturing feasibility through standard epitaxial growth processes.
Solution Approach 2:
The patent employs composite material structures including multiple layers of AlGaN and GaN with different aluminum compositions, nucleation layers, buffer layers, and various functional layers (shielding, insulating, contact layers). These composite structures optimize electrical properties, reduce defects, and enhance voltage withstand capacity by combining materials with complementary characteristics.
2Ease of manufacture
If Si substrates are used to reduce cost, then manufacturing cost decreases, but substrate defects and dislocations increase
Solution Approach 1:
The patent introduces multiple intermediary layers between the Si substrate and the active HEMT channels, including nucleation layers (AlN, AlGaN), buffer layers (GaN, AlGaN), and transition layers. These intermediary layers serve as mediators that gradually transition from the Si substrate lattice to the GaN-based channel layers, reducing lattice mismatch and dislocation propagation while maintaining the cost advantage of Si substrates.
Solution Approach 2:
The patent segments the substrate-to-channel transition into multiple distinct functional layers rather than using a single interface. The nucleation layer, buffer layers, and transition layers are separately optimized for different functions (lattice matching, defect filtering, electrical properties), allowing each segment to address specific substrate-related challenges independently.
3Reliability
If vertical HEMT structure with multiple layers is implemented, then voltage withstand and performance improve, but manufacturing process complexity increases
Solution Approach 1:
The patent designs layers with multiple functions to reduce overall process complexity. For example, the channel supply layer serves both as a structural layer and as the source of polarized charges that form the 2DEG. The gate electrode structure provides both electrical control and mechanical support. This multi-functionality reduces the number of separate manufacturing steps required.
Solution Approach 2:
The patent optimizes manufacturing by systematically varying material composition parameters (Aluminum content in AlGaN layers), thickness parameters, and growth conditions during epitaxial processes. These parameter changes allow precise control of electrical properties and defect densities without requiring fundamentally different manufacturing techniques, maintaining process compatibility while achieving superior device performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The vertical HEMT structure significantly improves voltage withstand capacity and reduces dark current, enabling performance comparable to HEMTs on intrinsic GaN substrates while using lower-cost Si substrates, with increased integration level and reduced parasitic capacitance.
Implementation Method 1
Polar semiconductors have many unique properties. Particularly importantly, fixed polarized charges are present at a surface of the polar semiconductor or at an interface of two different polar semiconductors. These fixed polarized charges may attract movable electrons or hole carriers and thus form the two-dimensional electron gas (2DEG)
Data Source
Figure 1~2A
Figure 2B~2C
Figure 2D~2F
AI summary
The present disclosure relates to a HEMT, which comprises a vertical interface; a channel layer disposed outside of the vertical interface; a channel supply layer disposed outside of the channel layer, wherein a vertical 2DEG is formed in the channel layer adjacent to an interface between the channel layer and the channel supply layer; a first electrode configured to be electrically connected to the vertical 2DEG; a second electrode configured to be electrically connected to the vertical 2DEG; a gate electrode disposed outside of the channel supply layer. The present disclosure also relates to a method of manufacturing a HEMT, which comprises forming a vertical interface; forming a channel layer outside of the vertical interface; forming a channel supply layer outside the channel layer, wherein a vertical 2DEG is formed in the channel layer adjacent to an interface between the channel layer and the channel supply layer; and forming a first electrode and a second electrode which are electrically connected to the 2DEG, and a gate electrode which form schottky contact to the 2DEG.